1. Field of the Invention
This invention relates to a method of killing microorganisms in the inside of a container. More particularly, this invention relates to a method of killing microorganisms by repeatedly sparking a focused, ultra-short-pulsed laser beam in the inside of such a container.
2. Description of the Prior Art
Killing of microorganisms, which when carried to totality constitutes sterilization, in containers into which are filled such substances as parenteral medications, foods, beverages, dairy products, and the like, has been practised for decades for the purpose of preventing the transmission of disease. Many methods have been devised to accomplish this purpose. Heat, both dry and wet, has been a popular method of killing microorganisms in the food, beverage and pharmaceutical arts for a long time. The use of chemicals such as formaldehyde, phenol, ethanol, ethylene oxide, and the like for killing microorganisms has found many useful applications. More recently irradiation, such as beta, gamma, and ultraviolet rays have been employed in specialized applications for killing microorganisms.
In 1968, U.S. Pat. No. 3,383,163 described a method of sterilizing the surface of a material which does not conduct electricity comprising contacting such surface with a gaseous plasma at an extremely high temperature. In this method a corona discharge was utilized to generate a plasma inside a container. The corona discharge was achieved by introducing a grounded electrode into the container, surrounding the container with a coil and pulsing from about 5000 to about 7000 volts and above into the coil. Exposure of the surface to a plasma for a very brief period of time, normally not longer than one-tenth of a second, is described.
In the time since U.S. Pat. No. 3,383,163 was issued, many attempts have been made to develop the plasma sterilization process into an economically feasible method because of the inherent advantage of killing the microorganisms in the inside of a container just prior to filling. However, the mechanical problems associated with introducing a grounded electrode into a container and simultaneously surrounding the container with a high voltage coil have been found to be of such a magnitude as to defeat exploitation of the invention. Moreover, the volume of plasma generated by the corona discharge is dependent on the style and shielding of the electrode tip, the winding of the high voltage coil and the potential difference between said electrode and said coil at the moment of the pulsed discharge, and such requirements have presented problems in the location of the electrode and coil so as to fill the container with plasma. Furthermore, the voltage required to initiate the corona discharge is substantial and requires specialized electrical circuitry.
Accordingly it is an object of this invention to provide a method of killing microoganisms in the inside of a container with a plasma which can be generated without the requirement for the mechanical introduction of an element into said container and the surrounding of said container with any element associated with said method.
Another object of this invention is to accomplish the killing of microorganisms in the inside of a container by generating a plasma in the inside of said container, said plasma not being required to contact the inside surfaces of said container to effect the microorganism kill.
Yet another object of the instant invention is to provide a method of killing microorganisms in the inside of a container irrespective of the electrical conducting properties of said container, by generating a plasma in the inside of said container.
Still another object of this invention is to kill microorganisms in the inside of a container by the repeated production of plasmas in the inside of said container.